Relationship between force and integrated EMG activity during voluntary isometric anisotonic contraction

Area of Science:

• Biomechanics
• Neurophysiology
• Human Motor Control

Background:

• Understanding the relationship between muscle electrical activity and generated force is crucial in biomechanics and motor control.
• Previous models often assumed a linear relationship between electromyogram (EMG) and force, which may not fully capture complex physiological mechanisms.

Purpose of the Study:

• To investigate the precise relationship between surface electromyogram (EMG) activity and the force generated by the extensor carpi radiales muscle during voluntary isometric anisotonic contractions.
• To determine if a non-linear model could better describe the input-output relationship of muscle contraction, considering EMG as input and force as output.

Main Methods:

• Surface electromyography (EMG) was recorded from the extensor carpi radiales in human subjects during voluntary isometric anisotonic contractions.
• The force generated by the muscle was measured concurrently with EMG.
• The relationship between force and integrated EMG (iEMG) was analyzed, considering both instantaneous and summed iEMG over time.

Main Results:

• The relationship between muscle force and instantaneous integrated EMG could not be accurately represented by a single linear function or a parabola.
• A non-linear, asymptotic function, specifically a double exponential function, was found to effectively model the relationship between force and summed iEMG.
• This suggests that muscle force generation is dependent on the cumulative EMG activity over the course of a contraction.

Conclusions:

• The relationship between muscle force and EMG is non-linear and asymptotic, challenging previous linear assumptions.
• A double exponential function provides a better fit, indicating two underlying mechanisms contributing to voluntary muscle force production.
• Considering summed iEMG, reflecting the history of muscle activation, is essential for accurately modeling muscle force output.